Re: [Boost-users] problems with Boost.Thread on VS10

Subject: Re: [Boost-users] problems with Boost.Thread on VS10
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2012-04-09 21:31:45

Le 10/04/12 02:10, Jeffrey Lee Hellrung, Jr. a écrit :
> On Mon, Apr 9, 2012 at 4:54 PM, Vicente J. Botet Escriba 
> <vicente.botet_at_[hidden] <mailto:vicente.botet_at_[hidden]>> wrote:
>
>     Le 10/04/12 01:24, Jeffrey Lee Hellrung, Jr. a écrit :
>>     On Mon, Apr 9, 2012 at 3:14 PM, Vicente J. Botet Escriba
>>     <vicente.botet_at_[hidden] <mailto:vicente.botet_at_[hidden]>> wrote:
>>
>>
>>
>>
>     The overload
>
>             explicit packaged_task(R(*f)()):
>                 task(new
>     detail::task_object<R,R(*)()>(f)),future_obtained(false)
>             {}
>
>     seems necessary because otherwise the task_object is instantiated
>     with <R,R()> which is not what we want.
>     Do you have an hint on how simplify this?
>
>
> Okay yeah I wasn't sure why you needed this overload, thanks for 
> clarifying. I guess when constructing a packaged_task with a function 
> name, and you don't explicitly use the address-of operator (&), F gets 
> bound as a function reference? Probably easiest to just explicitly use 
> a separate constructor as above and document its necessity.
>
>>
>>         The test futures/packaged_task/alloc_ctor_pass.cpp gives this
>>         context.
>>
>>         Thanks for your patience and perseverance.
>>
>>
>>     And thank you for clarifying the issue for me!
>>
>>
>     Please, could you check the patch and see if there is something
>     that can be improved.
>
>
> Yeah that looks about what I would've suggested. Just add, like you 
> said, the remove_cv's.
>

I have added some test for const and free functions.

Note, as you mentioned, the need to use & in (***1) when the function 
doesn't returns the packaged_task result type but something convertible 
to it.

With the following patch everything is OK.

It is a pleasure to work with you. I learn always something important :-)
Vicente

===============================================
tests
===============================================

double fct()
{
   return 5.0;
}
long lfct()
{
   return 5;
}

   {
       const A a(5);
       boost::packaged_task<double> p(a);
       BOOST_TEST(p.valid());
       boost::future<double> f = BOOST_EXPLICIT_MOVE(p.get_future());
       //p(3, 'a');
       p();
       BOOST_TEST(f.get() == 5.0);
       BOOST_TEST(A::n_copies > 0);
       BOOST_TEST(A::n_moves > 0);
   }
   {
       boost::packaged_task<double> p(fct);
       BOOST_TEST(p.valid());
       boost::future<double> f = BOOST_EXPLICIT_MOVE(p.get_future());
       //p(3, 'a');
       p();
       BOOST_TEST(f.get() == 5.0);
   }
   {
       boost::packaged_task<double> p(&lfct); // *** 1
       BOOST_TEST(p.valid());
       boost::future<double> f = BOOST_EXPLICIT_MOVE(p.get_future());
       //p(3, 'a');
       p();
       BOOST_TEST(f.get() == 5.0);
   }

===============================================
patch
===============================================

Index: boost/thread/future.hpp
===================================================================
--- boost/thread/future.hpp    (revision 77875)
+++ boost/thread/future.hpp    (working copy)
@@ -20,6 +20,7 @@
  #include <boost/type_traits/is_fundamental.hpp>
  #include <boost/type_traits/is_convertible.hpp>
  #include <boost/type_traits/remove_reference.hpp>
+#include <boost/type_traits/remove_cv.hpp>
  #include <boost/mpl/if.hpp>
  #include <boost/config.hpp>
  #include <boost/throw_exception.hpp>
@@ -1811,7 +1812,9 @@
  #ifndef BOOST_NO_RVALUE_REFERENCES
          template <class F>
          explicit packaged_task(F&& f):
-            task(new detail::task_object<R,typename 
remove_reference<F>::type>(boost::forward<F>(f))),future_obtained(false)
+            task(new detail::task_object<R,
+                typename remove_cv<typename 
remove_reference<F>::type>::type
+ >(boost::forward<F>(f))),future_obtained(false)
          {}
  #else
          template <class F>
@@ -1832,11 +1835,22 @@
  #endif

  #if defined BOOST_THREAD_PROVIDES_FUTURE_CTOR_ALLOCATORS
+        template <class Allocator>
+        packaged_task(boost::allocator_arg_t, Allocator a, R(*f)())
+        {
+          typedef R(*FR)();
+          typedef typename Allocator::template 
rebind<detail::task_object<R,FR> >::other A2;
+          A2 a2(a);
+          typedef thread_detail::allocator_destructor<A2> D;
+
+          task = task_ptr(::new(a2.allocate(1)) 
detail::task_object<R,FR>(f), D(a2, 1) );
+          future_obtained = false;
+        }
  #ifndef BOOST_NO_RVALUE_REFERENCES
          template <class F, class Allocator>
          packaged_task(boost::allocator_arg_t, Allocator a, F&& f)
          {
-          typedef typename remove_reference<F>::type FR;
+          typedef typename remove_cv<typename 
remove_reference<F>::type>::type FR;
            typedef typename Allocator::template 
rebind<detail::task_object<R,FR> >::other A2;
            A2 a2(a);
            typedef thread_detail::allocator_destructor<A2> D;